Method for purifying alcohols



March 4, 1952 B. ocoNNoR ET AL METHD FOR PURIFYING ALCOHOLS 2 SHEETS- SHEET `1 Filed April 26, 1949 usm @SEQ B. OCONNOR ETAL METHOD FOR PURIFYING ALCOHOLS March 'v4, 1952 2 SHEETS-SHEET 2 Filed VApril 26, 1949 Bcob mSG ESS@ A JNVENTORS:

Bue/l O'Connor Frank G Pearce By:A um 9- wat BSW @595B NON Patent n Agent Patented Mar. 4, i952 METHOD FOR PURIFYNG ALCOHOLS Buell OConnor and Frank G. Pearce, Tulsa,

Okla., assignors to Stanolind Oil and Gas Company, Tulsa, Okla., a corporation of Delaware application April 2s, 1949,`seria1 No. 89,636

(ci. aso-G43) 5 Claims.

This invention relates to the purification of alcohols. More particularly, it relates to the separation of alcohols from admixture with other organic compounds by the preparation, segregation, and decomposition of borate esters.

In the introduction of alcohols by various processes, the desired products are obtained in varying states of purity. Methanol, for example, is

commonly obtained in a high degree of purity by the reaction of hydrogen and carbon monoxide over certain catalysts, and ethanol is obtained in a readily purifiable form by the yeast-fermentation of various carbohydrates. Other processes, however, do not in general produce single products or products from which the individual constituents may readily be separated, For example, in the oxidation of normally liquid hydrocarbons according to various processes Well known in the art, products are obtained which consist of a wide variety of the original hydrocarbons and the oxygen-containing compounds derivable therefrom. As a further example, in the hydro genation of carbon monoxide according to the Fischer-Tropsch process and its numerous modifications, particularly in embodiments thereof employing alkali-promoted iron catalysts, a twophase product is obtained comprising water and virtually the entire range of saturated and unsaturated aliphatic hydrocarbons, primary al1- phatic alcohols, aliphatic ketones, and aliphatic i carboxylic acids. When the separation of such mixtures is attempted by fractional distillation, each fraction ordinarily comprises a complex mixture of hydrocarbons and organic oxygenated componuds, and further segregation of the components thereof is ordinarily not feasible by con ventional distillation methods.

It has heretofore been proposed to separate alcohols from admixture with other organic compounds by a boration process, in which a mixture of alcohols with non-esterifiable substances, such as hydrocarbons, ethers, heterocyclics, and the like, is treated with boric acid or boric anhydride under esteriiication conditions to produce the relatively high-boiling alcohol borates, from which the non-alcoholic impurities may readily be distilled. The borates may thereafter be hydrolyzed by conventional means to release the alcohols in relatively pure form. The basic boration process, however, when carried out in this way, is open to the objection that the boration procedure is relatively slow and expensive, and the recovery and recycling of the boric acid is complicated by the fact that it is released from the alcohol esters in lli the form of a dilute aqueous solution, or as a slurry in a saturated laqueous solution.

We have now discovered that the boration of an alcohol can be effected by treating it with a borate ester of another alcohol under radical-exchange conditions, and under conditions, to be set forth more fully hereinafter, such that the new borate ester produced thereby can be separated from the other constituents of the reaction mixture. The new borate ester is thereafter decomposed, and the original alcohol is liberated and recovered in puried form.

We have further discovered that the original alcohol can be liberated from the borate ester thereof and the borate ester of said other alcohol can be simultaneously regenerated and recovered by a novel operation in which the borate ester of the original alcohol is countercurrently contacted with said other alcohol under radical-exchange conditions and under conditions of temperature and pressure such that either said new borate ester or said other alcohol, whichever is lower boiling, is maintained in the vapor phase.

(For convenience, the original alcohol that is to be treated according to our invention will here inafter be termed the charge alcohol; after puriiication it will be the purified charge alcorhol; the ester employed in the esterication of the charge alcohol will be the process ester; the alcohol derivableV from the process ester will rbe the process alcohol and the esterified charge alcohol will be the charge-alcohol ester?) On the basis of these discoveries, we have devised a lnovel and highly advantageous process for the purication of alcohols, including the steps of esterifying an alcohol (the charge alc0hol) with a borate ester (the process ester) of another alcohol (the process alcoho1), separating the resulting charge-alcohol ester, coun- Vtercurrently contacting the charge-alcohol ester with the process alcohol, whereby the charge alcohol and the process ester are regenerated, and recycling the process ester.

One object of our invention is to purify alcohols. Another object is to separate alcohols from other organic materials. A further object is to separate alcohols from hydrocarbons, ethers, alldehydes, ketones, heterocyclic compounds, and the like, boiling at or near the boiling points of said alcohols. A still further object of our in .vention is to facilitate the conversion of alcohols into borate esters and the recovery of borate values from the resulting esters. Another object is to adapt the boration process for purifying alcohols to continuous operation. Other objects of our invention and its advantages over the prior art will be apparent from the following description and claims.

In the esterication step of our invention, the impure alcohol charging stock is heated with a process ester, said ester being a borate of another alcohol (the process alcohol) which has a boiling point sufficiently different from the boiling point of the charge alcohol to permit the two alcohols to be separated by fractional distillation. Ordinarily -a difference in boiling points of 5 to C. is suicient for this purpose. We prefer to use a process ester derived from an alcohol boiling 5 to 10 C. or more below the boiling'point of the charge alcohol. For example, in the purification of l-butanol and higher-boiling alcohols, trimethyl borate, triethyl borate, tripropyl borate, and triisopropyl borate may be used, as

well as the secondary butyl, isobutyl, and tertiary butyl borates. Triethyl borate is especially convenient. This ester, when heated with a higherboiling alcohol, undergoes rapid radical-exchange with the higher-boiling alcohol; and if the resulting ethanol is withdrawn from the reaction mixture, the reaction is driven rapidly to completion, Vgiving the desired borate of the higherboiling alcohol according to the following equation, where R. represents a C3 or higher hydrocarbon radical:

Itwill 'be apparent that we are not restricted in our choice of process esters to any one class of borate esters, but may use substantially any borate ester. For economic reasons, however, the ester should not tend to undergo degradation reactions or other side reactions under the radicalexchange conditions employed in our process.

When the esterication step of our invention is carried out with a process ester derived from a process' alcohol which boils above the charge alcohol, the reaction cannot be driven to completionby withdrawing the process alcohol, as

liberated, by conventional fractional distillation.

Instead the esterication is conveniently carried out Vby Vpassing the impure charging stock in vaporous form upward through a treating Zone under radical-exchange conditions countercurrentto a stream of process ester. The liberated i defined above, preferably the alcohol derivable from the process ester used in the esterication step. Where the radical exchange is eifected i' Awith ak process alcohol boiling above the charge alcohol, the reaction may be driven to completion by fractionally distilling the liberated charge alcohol from the reaction mixture. Where, however, the process alcohol boils below the charge alcohol, then the regeneration step may be 'carried out by passing the process alcohol in vapor form upward through a treatingr zone countercurrent to a descending stream of the purified charge-alcohol ester. TheY charge alcoholV is regenerated thereby in purified form, and emerges overhead, while the process ester is regenerated and is withdrawn from the bottom of the treating zone, from which it can be recycled.

In the esterication step of our invention, the molar ratio of process ester to alcohols in the impure charging stock should be at least about 033:1 and preferably somewhat higher, for example from 0.3521 to 0.411, in order to permit substantially complete conversion of the charge alcohols into borate esters.

In effecting radical exchange between the impure charging stock and the process ester in the first step of our invention, conventional process conditions may be used, well known in the art. The reaction may be effected, for example, at ordinary or at elevated pressures and at a temperature sufficiently high to maintain a vapor stream at the pressure employed, and to distill out the desired fraction. For example, a temperature above about 60 C. in the reaction zone is ordinarily suicient to produce a satisfactory rate of radical interchange, but higher temperatures, e. g. C. and above, are generally required to bring'the reaction mixture to reflux, even when operating with trimethyl borate as the process ester. A catalyst for the reaction is not required, but the reaction may be accelerated by incorporating in the'reaction mixture a catalytic amount, for example, around 1%A by weight, of a strong acid such as sulfuric acid, toluenesulfonic acid, propanesulfonic acid, phosphoric acid, or the like. The charging stock should preferably be substantially free from water, since any water present therein tends to hydrolize the process ester and to retard the formation of the desired charge-alcohol ester.

The regeneration of the charge alcohol and the process ester may be carried out under the general conditions used in the esterication step. For complete'regeneration of the process ester, the molar ratio of the process Ialcohol to the purified charge-alcohol ester should be at least 3:1, and preferably somewhat higher, for example 42'1 or more.

It will be apparent that the effectiveness of the boration process for purifying alcohols Vdepends on the conversion ofthe alcohols into ester-type derivatives boiling 'above the impurities present with the alcohol, so that the impurities may be fractionally distilled away from the y alcohol derivatives. As a preliminary to the boration process, it is therefore advantageous to subject the imp-ure alcohol charging stock to such subsidiary operation or operations as will remove any impurities boiling in the range of the borates of the alcohols. This may suitably be done by subjecting the impure alcohol to a preliminary fractional distillation and separating the alcohol as a distillate fraction of relatively narrow boiling range, substantially free from higher-boiling impurities that might contaminate the esters subsequently to be fonnedl Mixtures of alcohols, such as the oil phase obtained in the oxidation of hydrocarbons or in the hydrogenation of carb-on monoxide in the presence of an alkali-promoted iron catalyst, may advantageously be separated by' fractional distillation into a series of` fractions of narrow boiling range, each of which may then be subjected to the boration. process.

It will be further apparent that the operative- -ness of the radical-exchange process for the boration and purification of an impure alcohol depends on the use, for the initial radical-exchange step, of the borate ester of an alcohol wherein the alcohol boils sufficiently far from the impure alcohol to permit the separation thereof, preferably by fractional distillation. For this purpose, it is ordinarily sucient if the process alcohol boils around 5 to 10 C. above or below the charge alcohol.

In eifecting the initial radical-exchange step of our process, we prefer to utilize a borate ester of the specific process alcohol to be used subsequently in the regeneration of the charge alcohol. This facilitates the design and operation of the process, since it simplies the matter of recovery and recycle of the various process materials. In View of the foregoing description, however, it will be apparent that out process is not limited to such an embodiment,'but is applicable broadly as herein set forth.

In an advantageous embodiment of our invention, applied to the treatment of the organic stream obtained in the hydrcgenation of carbon monoxide, the borate esters obtained from one boiling-range fraction thereof may be used to effect the boration of another fraction, while simultaneously regenerating the purified alcohols from the first fraction. This procedure may be repeated at will on further fractions, so that the necessity for providing a special process ester is obviated.

Our process is suitable for the purification of alcohols in general, and is especially well adapted to the puriiication of alcohols having from one to twenty carbon atoms in the molecule. While we have obtained excellent results in the purification of aliphatic primary monohydric alcohols, our process is not limited thereto, but is also applicable to the treatment of aliphatic, cyclo-l aliphatic, and aromatic alcohols, primary, secondary, and tertiary, monohydric and polyhydric, saturated and unsaturated, and of alcohols wherein the hydrocarbon radical is a combination of aliphatic and/or cycloaliphatic and/or aromatic groups. Our process is suitable, for example, for the purication of isopropyl alcohol, 1butanol, tertiary amyl alcohol, Z-ethyl-l-hexanol, capryl alcohol, l-decanol, cetyl alcohol, stearyl alcohol, crotyl alcohol, ethylene glycol, 1, 3-butanediol, glycerol, cyclohexanol, B-methylcyclohexanol, phenol, betanaphthol, benzyl alcohol, resorcinol, and the like.

The first of the attached ilowsheets, Figure 1, illustrates an embodiment of our invention employing two extractiva distillation operations to effect the desired interchanges of organic radicals, and employing a process ester derived from a process alcohol boiling below the charge alcohol.

A dry, impure alcohol stream, suitably a fraction of restricted boiling range obtained from the oil stream produced by the hydrogenation of carbon monoxide in the presence of a uidized, alkali-promoted iron catalyst, is introduced through line |0|, heater |02, and line |03 into the top of fractionating column (extra.ctive still) |04, equipped with reboiler |05. Therein, it flows downward countercurrent to a vaporous stream of borate process-ester, derivable from an alcohol boiling below the charge alcohol, and introduced into a lower intermediate section of the column through line |06. Makeup process ester is supplied as needed through line |01, heater |00, and line |09, preferably to a somewhat lower section of column |04, and the total quantity'of process ester entering column |04 is somewhat in excess of the stoichiometric quantity required to convert all of the alcohols in the impure alcohol stream into borates. The bottom of column |04 is operated at a temperature suiiciently high, suitably above about C., to boil substantially all process alcohol and process ester therefrom, and the column is operated under a suiiicient pressure to permit such temperature therein. Under these conditions, substantially complete radical interchange between the impure alcohols and the process ester takes place, with the ref sult that a vaporous process-alcohol stream containing more or less process ester, depending on the excess ester entering the column, emerges overhead through line I0, and a treated charging stock wherein the charge alcohols are now present as the borate esters emerges from the bottom of the column through line The treated charging stock is transferred by pump ||2 through line 3, heater ||4, and line ||5 into an intermediate section of fractionating column. IIB, equipped with reboiler ||1. Therein, the charge-alcohol borates are stripped substantially free from the impurities originally present in the charging stock, and are withdrawn in purified form from the bottom of the column through line H8. The lower-boiling impurities, including hydrocarbons, aldehydes, ketones, ethers, and the like, are taken off overhead through condenser 9 into reflux drum |20, from which a portion is refluxed to the top of the column through valved line |2|, and the remainder is withdrawn through valved line |22.

The vcharge-alcohol borates in line ||8 are transferred by pump |23 through line |24, heater |25, and line |26 into the topof fractionating column (extractive still) |21, equipped with reboiler |28. Therein, it iiows downward countercurrent to a vaporous stream of process alcohol, introduced into a lower intermediate section of the column through line |29, heater |30, and line 13|. Makeup process alcohol is supplied as needed through line |32, heater |33, and line |34, preferably to a somewhat lower portion of column |21. Radical interchange takes place within column |21 under substantially the same conditions employed in column |04, with the result that substantially all of the charge-alcohol borates entering the top of the column are decomposed, and the charge alcohols are regenerated and withdrawn from the bottom of the column through line |35, cooler |36, and line |31 to storage or to further processing to isolatethe individual constituents thereof. A mixture of process ester and a quantity of process alcohol, depending on the quantity of excess process alcohol entering the bottom of the column, emerges overhead from column |21 through line |38.

The overhead streams from columns |04`and |21 are further processed in fractionating column i39, equipped with reboiler |40. The mixture of process alcohol and process ester in line Hi), ordinarily predominantly process alcohol, is led through heater |4| and line |42 into an upper intermediate section of column |39; and the mixture of process ester and process alcohol in line i38, ordinarily predominantly process ester is led through heater |43 and line |44 into a lower intermediate section of column |39. Within the column, the alcohol and the ester are separated. The alcohol is distilled overhead through condenser |45 into reux drum |46, from which a portion is reuxed to the column through valved line |41, and the remainder is recycled to column |21 through valved line |29, heater |30, and line |3|. The process ester ows from the bottom o'f column TI38 through line 1I48, and-is recycled vby pump y I49 through -line `V|53, heater I 5I andline IUB'to'colu'mniI'M.

lFigure 2 illustrates fan r'advantag'eous embodimen-tlof our inventionfemp'loying-a process ester derivedfroma process alcohol boiling above the charge alcohol. In this embodiment, Vthe zinitial radical exchange betweenthe charge alcohol vand the process ester, and the-'separatio'nof impurities "from the `resulting charge-'alcohol ester, 'are carried'o'ut 'simultaneously in a single extractive still.

An impure alcohol charging stock is introduced through linefZDIjvaporizer v202,-and'lin`e 253 into a -lower section of fractionating column eiitractive still) `204, equipped 4with reboiler 205. The resulting stream of vaporous chargingstock flowsup'wa'rd through' the column and is countercurrently contacted with a hot, liquid streaml of a'pro'cess'ester-a berate ester of an alcohol (the process alcohol) boiling higher than the 'charge alcohol. The process ester is introduced into' an upper section of fractionating column 204 through line G, and makeup process ester is supplied as required'to the's'ame or `a neighboringse'cti'on of the column through line 201, heater 208,and line 209. Within column 204 two effects occur. kRadical exchange takes place betweenthe charge lalc'ohol and `the 'process ester, liberating the process alcohol; vand the vimpurities vin the charging stock, being lower-boiling than lthe esters present within the column, are distilled overhead in combination'with theliberated process alcohol. `From the bottom of column 204 through line 2 I 0 emerges a'stream of 'charge-alcohol'ester, together' with'any unchanged process ester. The vaporous stream 'of impurities and process alcohol emerging overhead'from column 204 ows into 'condenser'zl I ,fand the resulting condensate owsinto reflux dr'urnZIZ, from which a portion is reiiuxed fthrough valved line 2I3 to V1the top of column`2l4,`while the remainder iswithdra'wn through valved line 2 I`4.

Theimixture fof impurities and process alcohol n'valved line2'l4`is led Vthrough heater'ZI 5 land line 2I6 into an intermediate section of `fractionating-column 2 Il', equipped'with reboiler ZIB. 'Iherein, vthe impurities 'are fractionally distilled overhead throughcondenser 2 I9 intorefluxidrum 220,"i`rom which a portion `are refluxed to 'column A2I'I through valved line '22I,"and the 'remainder-are 'withdrawn through valved line222. From the bottom of fractionating column `2I1 a stream of purified Iprocess alcohol emerges through line 223.

The mixture of charge-alcoholiesten and process ester in line c2H) is transferred bypump 224 through line 225, heater 226,'and line 221 into an upper section of fractionating column (eX- tractive still) 228. The Ystream of process Va1- cohol `in line 223 is combinedin line 229 with makeup process alcohol, supplied through line 230, and the mixture 'is transferred by pump 23| through line 232, vaporizer 233, and line 234 into a lower section of fractionating column '228. Within column 228, the Vaporsof the process a1- cohol pass'upward countercurrent to the descending stream of charge-alcohol ester. Radical interchange between the two streams takes place,

regenerating the process ester-and liberatingthe charge alcohol in ypurified form. VThe purified charge alcohol emerges overhead from column 223 through condenser 235'i'ntoreuX-drum 23B, from which a'portionis reluxed throughvalved line .231 to the topof column '228 torepress the lil 8 simultaneous distillation of any esters, Vwhich would-contaminate the charge alcohol, -and the remainder of the overhead stream is withdrawn through'vvalved line 238 as the desired purified product.

.From thebottom of column 228 through line 239 emerges a stream of regenerated process ester, which is recycled by pump 240, line 24|, heat exchanger 242,andline 206 to 'column 204.

In the foregoing embodiment of our invention, the Y'process ester 'should, additionally be chosen so fth'at the process-alcohol constituent thereof has "a boiling pointwhich diiers at least'about 5 to 10 Cf'from the boiling point of the nonalcoholic impurities contained in the charging stock, in order to permit the separation of the process alcohol from the charging-stock impurities in fractionating column 2 I l. The methodlillustrated-in Figure 2 employs a process -alcohol boiling above the impurities, so that the process alcohol emerges from the bottom of fractionating column 2 I 'I. Where the process alcohol boils below the impurities, it will be apparent that the process alcohol and the impurities will emerge respectively from the top and the bottom of the column, without otherwise altering the manner in which-the process is carried out.

The following specic example illustrates the application of our invention to the isolation of l-octanol.

279-ml. portion of impure l-octanol containing 1.76 gram-moles of the alcohol was commingled with 47 ml. of triethyl borate, and the mixture was fractionally distilled. A first distillate fraction measuring '49 ml. and consisting essentially `of ethanol was withdrawn. Thereafter, a second distillate fraction was withdrawn, comprising the lexcess l-octanol present in the charge. This fraction measured 133 ml. and contained 0.84 gram-mole of the alcohol.

The distillation residue, measuring 131 ml. and comprising predominantly trioctyl borate, was passed downwardthrough a column having an inside diameter of 0.71 inch and a total length of ve feet, packed with single-turn 'glass helicesr while upward through the column, countercurrent to the descending stream of distillation residue, owed a vaporous stream of ethanol, supplied from a reboiler at the base of the column. The temperature of the system ranged from C. in the reboiler to 100 C. at the top of the column. A total volume ratio of ethanol to higher-alcohol borate of 3.5 was used. A vaporous stream comprising essentially triethyl borate and ethanol was taken 01T overhead and was condensed Yand analyzed. The condensate measured 500 m1. and contained 2.4% by volume of triethyl borate. The bottom product was fra'ctionally distilled to separate the puriiied alcohols therefrom. By this means 34 m1. ofsubstantially pure 1octanol were' recovered.

While lwe have illustrated our invention with certainspecicembodiments thereof, it is to be understood that we are not limited thereto. Our

invention is applicable broadly within the scope ester of another alcohol, which improvement comprises effecting said radical interchange by countercurrently contacting an alcohol with a borate ester of another alcohol in a distillation zone under extractive distillation conditions, and separately withdrawing from said distillation zone the alcohol and the borate ester resulting from said radical interchange.

2. An improvement in the boration process for purifying a, crude alcohol employing radical interchange with a borate ester of another alcohol, said crude alcohol having a boiling point lower than said ester, which improvement comprises eiecting said radical interchange by countercurrently contacting a vaporous stream of said crude alcohol with a liquid stream of said borate ester in a distillation Zone under extractive distillation conditions, and separately withdrawing from said distillation Zone said other alcohol and` a borate ester of said crude alcohol as distillate and bottoms streams in accordance with the relative boiling points thereof.

3. An improvement in the boration process for purifying a crude alcohol employing radical interchange with a borate ester of another alcohol, said crude alcohol having a boiling point higher than said ester, which improvement comprises effecting said radical interchange by countercurrently contacting a vaporous stream of said borate ester with a liquid stream of said crude alcohol in a distillation zone under extractive distillation conditions, and separately withdrawing from said distillation zone said other alcohol and a borate ester of said crude alcohol as distillate and bottoms streams in accordance with the relative boiling points thereof. l

4. An improvement in the boration process for purifying a crude alcohol employing radical interchange with another alcohol for regenerating the purified alcohol from a purified borate ester thereof, said other alcohol having a boiling point lower than said ester, which improvement comprises efecting said radical interchange by countercurrently contacting a vaporous stream of said other alcohol with a liquid stream of said purified borate ester in a distillation zone under extractive distillation conditions, and separately Withdrawing from said distillation zone said purified alcohol and a borate ester of said other alcohol as distillate and bottoms streams in accordance with the relative boiling points thereof.

5. An improvement in the boration process for purifying a crude alcohol employing radical interchange with another alcohol for regenerating the purified alcohol from a purified borate ester thereof, said other alcohol having a boiling point higher than said ester, which improvement comprises effecting said radical interchange by countercurrently contacting a vaporous stream of said purified borate ester with a liquid stream of said other alcohol in a distillation zone under extractive distillation conditions, and separately withdrawing from said distillation zone said puried alcohol and a, borate ester of said other alcohol as distillate and bottoms streams in accordance with the relative boiling points thereof.

BUELL OCONNOR. FRANK G. PEARCE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,886,885 Kaufmann Nov. 8, 1932 2,068,415 Klipstein Jan. 19, 1937 2,088,935 Vaughn Aug. 3, 1937 OTHER REFERENCES Schilf: Annalen, Supplement, vol. 5, 18'7 

1. AN IMPROVEMENT IN THE BORATION PROCESS FOR PURIFYING A CRUDE ALCOHOL EMPLOYING RADICAL INTERCHANGE BETWEEN AN ALCOHOL AND A BORATE ESTER OF ANOTHER ALCOHOL, WHICH IMPROVEMENT COMPRISES EFFECTING SAID RADICAL INTERCHANGE BY COUNTERCURRENTLY CONTACTING AN ALCOHOL WITH A BORATE ESTER OF ANOTHER ALCOHOL IN A DISTILLATION ZONE UNDER EXTRACTIVE DISTILLATION CONDITIONS, AND SEPARATELY WITHDRAWING FROM SAID DISTILLATION ZONE THE ALCOHOL AND THE BORATE ESTER RESULTING FROM SAID RADICAL INTERCHANGE. 